By default, ceiling lights are set to snap to ceilings, and wall lights are set to snap to walls. Lamps have no snap setting so that you can place them anywhere in a room. You can change a light fixture’s snap setting on the fixture’s Behavior property page. Note that this applies to interior light fixtures only.
To change the way a light snaps on insertion:
In the catalog, select the light fixture whose snap setting you want to change.
Right-click and select Catalog Manager. You can also access the Catalog Manager by selecting File > Catalogs > Catalog Manager.
In the Catalog Manager dialog, make sure the correct fixture is selected, then select Catalog > Element Properties.
In the Lights dialog, select the Behavior tab.
From the Snap Light to drop box, select either Ceiling, Wall or None.
Click OK in the Lights dialog.
Click OK.